Method for the production of multilayer metal blanks

ABSTRACT

A method for producing metal blanks comprising several layers of the same or of different metals; including the steps of pouring liquid metal in batches into a mould previously charged with a slag mixture functioning to protect the surface of the metal; each subsequent pour of metal after the first one, being delivered into the mould after the horizontal surface of a preceding pour has become coated with a support crust of a solid metal; the temperature of the support crust formed being higher than the melting point of the protective slag mixture, but lower in temperature than the crystallization temperature of the metal poured.

United States Patent [191 Piven et al.

[ June 28, 1974 METHOD FOR THE PRODUCTION OF MULTILAYER METAL BLANKS 22 Filed: 1 Dec. 4, 1972 211 Appl. No.: 311,646

Related US. Application Data [63] Continuation of Ser. No. 132,601, April 8, 197 1,

1,707,117 3/1929 Foster 164/95 1,831,310 11/1931 Lindemuth 164/96 X 2,493,394 l/195O Dunn et a1. 164/134 X 3,395,747 8/1968 Thompson 164/95 Primary Examiner-R. Spencer Annear Attorney, Agent, or Firm-Holman & Stern 5 ABSTRACT A method for producing metal blanks comprising several layers of the same or of different metals; including the steps of pouring liquid metal in batches into a mould previously charged with a slag mixture functioning to protect the surface of the metal; each subsequent pour of metal after the first one, being delivered into the mould after the horizontal surface of a preceding pour has become coated with a support crust of a solid metal; the temperature of the support crust formed being higher than the melting point of the protective slag mixture, but lower in temperature than the crystallization temperature of the metal poured.

2 Claims, No Drawings blanks are designed for further processing on presses or rolling mills to convert them into metal sheets or sections.

Known in the prior art is a process for fabricatingmetal blanks by feeding the liquid metal in batches into a mould charged in advance with a slag mixture intended to protect the surface of the metal. With the above technique, each subsequent portion ofthe liquid metal is fed into the mould when the side faces of an ingot are coatedwith a skin of solid metal sufficiently strong to withstand the stresses originating when the ingot is drawn out of the mould. In addition, the preceding portion of the metal is heated from the side the liquid'metal is fed, with a view to provide a small pool of the molten metal on the horizontal surface of the liquid metal. In this procedure the blank is formed from the batches-of the molten metal having a liquid boundary line and therefore intermixing before crystallization. I

Due to the accelerated crystallization, the'blanks produced by the technique described incorporate Generally,'the'above method is relatively expensive and does not lend itself to mass production of uniform multilayer blanks.

Occasionally coolers, generating additional centres of crystallization, are fed to improve the structure of a metal blank, the introduction of such coolers into the liquid metal presents a serious difficulty, associated, in particular, with thenecessity for uniform distribution of the coolersthroughout the blank. This calls for the production of both the Coolers and appropriate apparatus to disperse them uniformly in the metal, which makes the process evenmore expensive.

The multilayer blanks are also manufactured by using a cast-cladding process; With this method, a metal sheet must be prepared to act as a blank cladding layer; it is also necessary to have a device for cleaning the blank cladding layer treating its surface with chemical reagents; and coating it with fluxes to protect the metal from the oxidizing influence of the atmosphere. Upon processing, the sheet is placed in a mould and the liquid metal is poured, until the mould is brim-full, contact between the liquid metal and metal sheet assures weldability between the blank layers during the subsequent hot pressure treatment thereof. Crystallization of the blank, between the layers of crystallizing metal and the metal sheet gives rise to the internal stresses related to the different physical state. This results in the formation of internal cracks in the crystallizing metal and in the exfoliation of the blank layers.

The need for preliminary preparation of metal sheets in producing multilayer blanks coupled with a lengthy production cycle and inadequate quality of the blanks, obtained, make the foregoing method expensive.

Also known are methods for fabricating multilayer blanks which are'based .on the application of a welding process and ensure high weldability of the blank layers and a reduction in cracking. In this case, the metal sheet employed for the production of blanks are first machined, and there after a layer of another metal is applied on the sheets.

In diffusion hot-pressure welding, adequate weldability of layers is achieved by processing their contact surfaces to obtain a high degree of cleanliness and by protecting them against an adverse effect of an oxidizing atmosphere for this procedure, special apparatus and devices are mandatory.

Further methods of manufacturing multilayer blanks through the use of this welding procedure require high metal consumption, long production cycle and expenses, beingtherefore inefficient.

It is an object of the present invention to eliminate the shortcomings of the prior art.

The present invention is, in essence, directed to providing a method for producing metal blanks, more efficiently as compared with known methods, producing an improved blank structure, and enhancing the joint strength between bonding of the blank layers.

This object is achieved by providing a technique for the manufacture of metal blanks by feeding liquid metal in batches into a mould which had been filled beforehand with a slag mixture; designed to protect the surface of the metal, in which technique, according to the present invention, each succeeding pour after the first one, the liquid metal is poured into the mould after the horizontal surface of the preceding portion is coated with a crust of solid metal at a temperature higher than melting point of the slag mix, but lower than the crystallization temperature of the metal being poured into the said mould so that the slag continues to perform its protective function.

This technique facilitates mass production, tends to reduce technological losses or waste metal, decrease the length of the production cycle required for the manufacture of a blank, and is accordingly more efficient than the prior art processes.

Metal blanks, produced through the use of this novel method incorporate an improved structure and enhanced adhesion between the layers forming the blank.

It is advisable that the weight of the first batch of the metal, poured into the mould, be from 10 to 20 percent of the total blank weight, whereas the weight of each following batch or pour range within to percent of the weight of the preceding batch.

The foregoing relation between the weights the metal batches, poured, makes it possible to reduce the crystallization time between subsequent portion of the metal, forming the blank layer.

The present invention was carried out in ascribed below in an exemplary embodiment conforming to the following steps.

A cast iron mould, preferably with a refractory lining, is charged with a slag mixture. The latter may be in the form of a powder or a melt, in its fluid state, in amounts ensuring protection of the metal surface from oxidation. The first batch of the liquid metal, constituting from 10 to 20 percent of the total blank weight, is poured into the mould filled with the slag mix. The temperature of this first batch is sufficient to melt down the slag mixture, if it is in a pulverized form. The poured metal descends in the mold and the slag floats up, protecting the entire surface of the poured metal batch from oxidation. At that moment, the metal, poured into the mould, cools down and starts crystallizing at the mould walls, whereupon, the horizontal surface of the metal batch, which has been poured into the mould, is covered with a crust formed of hard metal, sufficiently strong not to be crushed by the next portion poured into the mould.

The presence of the crust may be is determined either by a conventional filler, or where automatic controls are available, by temperature records taken in each upper layer of the metal batch, poured. The temperature will be higher than the melting point of the slag mixture, but lower than the crystallization temperature of the metal to be poured. The weight of each subsequent portion of the liquid metal is reduced in weight so that it ranges within 80 to 95 percent of thatof the preceding portion. Each metal batch is poured in relation to the temperature ratio at which the already poured batch is coated with a horizontal skin which remains intact when the next lot of the liquid metal is poured on it.

A six-ton blank, cast according to the novel method, had less pronounced liquation and segregation contrary to the blanks produced by conventional methods. Analysis of the novel test blank demonstrated adequate weldability or adhesion of its layers without any displacement, and a smooth surface suitable for further processing on rolling mills.

What is claimed is:

1. A method for producing metal blanks comprising the following steps of: charging a mould for the fabrication of the metal blanks with a protective slag mixture functioning to protect the surface of the metal blank being produced; feeding a first batch of the metal into the said mould, containing the slag mixture; feeding subsequent batches of liquid metal, after the first one, after the horizontal surface of the preceding has cooled to produce a skin of solid metal at a temperature higher than the melting point of the slag mixture and lower than the crystallization temperature of the preceeding batch of metal poured.

2. The method, as claimed in claim 1, in which the weight of the first batch of metal poured into the mould constitutes from 10 to 20 percent of the total weight of the blank, and the weight of each subsequent batch poured ranges within to percent of that of the preceding batch poured. 

1. A method for producing metal blanks comprising the following steps of: charging a mould for the fabrication of the metal blanks with a protective slag mixture functioning to protect the surface of the metal blank being produced; feeding a first batch of the metal into the said mould, containing the slag mixture; feeding subsequent batches of liquid metal, after the first one, after the horizontal surface of the preceding has cooled to produce a skin of solid metal at a temperature higher than the melting point of the slag mixture and lower than the crystallization temperature of the preceeding batch of metal poured.
 2. The method, as claimed in claim 1, in which the weight of the first batch of metal poured into the mould constitutes from 10 to 20 percent of the total weight of the blank, and the weight of each subsequent batch poured ranges within 80 to 95 percent of that of the preceding batch poured. 